Determination of thorium and uranium at the nanogram per gram level in semiconductor potting plastics by neutron activation analysis

A method was developed to determine thorium and uranium in semiconductor potting plastics. The method is based on neutron activation and subsequent radiochemical separation to isolate and permit measurement of the daughter products²³³Pa and²³⁹Np of the induced²³³Th and²³⁹U. These plastics typically contain macro amounts of silicon, bromine and antimony and nanogram per gram amounts of thorium and uranium. The radiochemical method provides the necessary sensitivity and makes it possible to easily attain adequate decontamination of the tiny amounts of²³³Pa and²³⁹Np from the high levels of radioactive bromine and antimony.Deceased     

Radiochemical separation of bismuth activities using Dalzin,and its application to geological problems

A radiochemical method has been devised for the separation of bismuth activities of the natural series,viz.²¹⁴Bi,²¹⁰Bi and²¹²Bi, and applied to the indirect estimation of their corresponding precursors,²²²Rn,²¹⁰Pb and²¹²Pb, in a wide variety of geological materials. The method consists of the solvent extraction of bismuth in radiochemically pure form from the sample solution atpH 2 with diallyldithiocarbamido-hydrazine (Dalzin) in chloroform, and back extraction with 2M acid. The advantages of this method over the dithizone extraction system are discussed.     

Anion exchange method for the sequential determination of uranium,thorium and lead-210 in coal and coal ash

A radiochemical procedure is presented for the sequential determination of uranium isotopes, thorium isotopes, and²¹⁰Pb in coal and coal ash. This procedure consists of dry ashing the sample, a nitric—hydrofluoric acid dissolution, removal of iron with ether extractions, and separation of the elements of interest by anion exchange chromatography. Uranium and thorium isotopes are measured by alpha spectrometry, while²¹⁰Pb is measured by beta counting its daugther activity,²¹⁰Bi. For 10 g coal samples and 1 g ash samples, the chemical yields for the radioactivities measured were 70–80%, and the relative standard deviations for replicate analyses were generally less than 9%. The deviations of the means from the reference values were within the combined errors of each and were usually less than ±5%. Minimum detectable activities were about 0.02 pCi for uranium and thorium isotopes and 0.2 pCi for²¹⁰Pb.     

Determination of alpha-emitting isotopes of uranium and thorium in vegetables and excreta

A radiochemical procedure for the determination of alpha-emitting isotopes of uranium and thorium in vegetables and excreta has been optimized, involving sample dissolution, separation by ionic exchange resin, electrodeposition and alpha-spectroscopy. Uranium and thorium isotopes were determined separately to prevent interference of ²²⁸Th from ²³²U tracer with ²²⁸Th from natural series of 232Th. This procedure was applied to faeces from people living in the Poços de Caldas plateau, a high natural radioactivity region of Brazil, and vegetables from the Laboratory of Environmental Monitoring (EML/DOE). Results show a chemical recovery of 80–95% for uranium and 46–72% for thorium.     

Analytical methods for the characterization and the leachability evaluation of a solid waste generated in a phosphoric acid production plant

Naturally Occurring Radioactive Materials (NORM) are present in the environment and can be concentrated by technical activities, particularly those involving natural resources. These NORM deposits are highly stable and very insoluble under environmental conditions at the earth's surface. However reducing or oxidant conditions or pH changes may enable a fraction of naturally occurring radionuclides to eventually be released to the environment. In this paper the analytical methods to determine the chemical and radiochemical composition of a solid waste generated in an acid phosphoric production plant was shown. The sample, analysed by gamma spectrometry and radiochemical methods, contained ²¹⁰Pb and ²¹⁰Po and a high activity concentration of uranium isotopes but it shows a very low quantity of ²²⁶Ra. Also a sequential extraction method consisting of five operationally-defined fractions was used to evaluate the leachability of uranium isotopes, ²¹⁰Pb and ²¹⁰Po. The average leaching potential observed in the sample is 97.6% for ²³⁸U, 93.2% for ²¹⁰Pb and 82.4% for ²¹⁰Po. Moreover the results show that ²¹⁰Pb and ²¹⁰Po are leachable under only extreme conditions, whereas uranium is very more soluble.     

Rapid separation of212Pb−212Bi−208Tl by high-performance liquid ion chromatography

Fast radiochemical separation of carrier-free²¹²Pb–²¹²Bi–²⁰⁸Tl in radioactive equilibrium was performed using the HPLC technique with an ion-exchange column /ION-210 for cation exchange, ION-110 for anion exchange and C18 loaded with cation-exchange sites/. Optimal results are obtained with the ION-110 column.²⁰⁸Tl and²¹²Pb are eluted by 0.5M HCl in 2.5 and 5 min, respectively.²¹²Bi is recovered by elution with 1M HNO₃.     

Thorium determination in a liver autopsy sample via direct γ-spectrometry and neutron activation analysis

Thorium was determined in a liver autopsy sample from a person treated with Thorotrast ca. 40 y earlier. The decay products²²⁸Ac,²²⁴Ra,²¹²Pb,²¹²Bi, and²⁰⁸Tl from the²³²Th series were identified by direct -spectrometry. Instrumental neutron activation analysis yielded a value of ca 22 g thorium per kg dry liver material. The total radiation dose to the whole liver was estimated in the order of 16 Gy.     

Transfer of210Pb and210Po to the environment during mining and processing of uranium ores

Transfer of²¹⁰Pb and²¹⁰Po from an uranium mine and mill to the environment was studied by measuring their concentrations in different stages of uranium extraction technology, in waste products from the mill and in environmental waters. A slightly modified radiochemical method was used for²¹⁰Po and²¹⁰Pb determination.     

Radiochemical separation of lead by amalgam exchange

An amalgam exchange technique has been used for the rapid radiochemical separation of lead. A number of variables which affect the exchange were studied and a lead yield of 88.5 %was obtained. At room temperature the procedure requires about 13 min, whereas at 40 degrees it can be completed in about 9 min. Radioactive tracers of 16 different elements were used to check the selectivity of this procedure, which has also been applied for the separation of (212)Pb from thorium nitrate solution.     

Determination of radioactive nuclides of uranium and thorium series and estimation of α-flux in LSI constituent materials

Gamma-rays of nuclides of uranium and thorium series in silicone resin and ceramics were measured with a Ge(Li) detector. The state of radioactive equilibrium was determined by comparing the concentrations of uranium and thorium with the radioactive concentrations of²¹⁴Pb and²¹²Pb. The radioactive equilibrium was attained in silicone resin but not in ceramics. The -flux was calculated from the concentrations of uranium and thorium and their daughter nuclides. The calculated values of -flux agreed with that of -flux measured.     

239+240Pu and137Cs distributions in seawater from the Yamato Basin and the Tsushima Basin in the Japan Sea

Comparative studies between column and batch liquid emulsion membrane techniques based on HDEHP/HCl system were carried out to develop a system for isolation of²³⁴Th from natural uranium. For column investigations a spray column was constructed and used with two different modes. In the first mode the feed solution was circulated through the membrane while in the second mode the membrane phase was circulated through the feed solution. The results showed that, kinetically, the equilibrium for thorium separation using batch technique is faster than the continous column system. Quantitative permeation of thorium was achieved within one minute of mixing whereby the permeation of uranium reached equilibrium after 3 minutes with a permeation percentage less than 6%. A procedure was developed to separate²³⁴Th from natural uranium with high radiochemical purity of more than 98%.     

Investigation of radioactive lead,uranium, and thorium in environmental waters by extraction chromatography resins

A time-saving and sensitive method for monitoring low concentration (activities) of ²¹⁰Pb, ²³²Th, and ²³⁰Th and ²³⁸U, ²³⁴U, and ²³⁵U in water samples has been developed. Through the combination of co-precipitation and extraction chromatography by 3M RAD disks and UTEVA (Eichrom) columns effective radiochemical separation of the analytes was carried out. Thorium and uranium activities were determined by alpha spectrometry and lead activity by LSC, respectively. The minimal detectable activities obtained were 0.6?Bq?m^?3 for uranium, 0.29?Bq?m^?3 for thorium, and 2.5?Bq?m^?3 for ²¹⁰Pb. More than 150 different waters were analysed for uranium content and only 30 for lead and thorium. The investigations are still in progress.     

Determination of isotopic thorium in biological samples by combined alpha-spectrometry and neutron activation analysis

The determination of isotopic thorium by alpha-spectrometric methods is a routine practice for bioassay and environmental measurement programs. Alpha-spectrometry has excellent detection limits (by mass) for all isotopes of thorium except²³²Th due to its extremely long half-life. This paper reports a pre-concentration neutron activation analysis (PCNAA) method for²³²Th that may be performed following alpha-spectrometry if a suitable source preparation material is utilized. Human tissues and other samples were spiked with²²⁹Th and the thorium was isolated from the sample using ion exchange chromatography. The thorium was then electrodeposited from a sulfate-based medium onto a vanadium planchet, counted by alpha-spectrometry, and then analyzed for²³²Th by neutron activation analysis. The radiochemical yield was determined from the alpha-spectrometric method. Detection limits for²³²Th by this PCNAA method are approximately 50 times lower than achieved by alphaspectrometry.     

Determination of thorium,uranium and plutonium isotopes in atmospheric samples

A new procedure for the radiochemical measurements of thorium, uranium and plutonium in atmospheric samples is described. Analysis involves coprecipitation of these actinides with iron hydroxide from a 40-to 50-dm³ sample of rainwater, followed by radiochemical separation and purification procedures by the use of ion exchange chromatography (Dowex AG1×8) and solvent extraction. The new procedure enables one to determine the isotopes of thorium, uranium and plutonium, which are found in rainwater at extremely low concentrations, with a chemical yield ranging from 60 to 80%.     

A Radiochemical Method for Selective Determination of Traces of Lead

Abstract

A very simple and rapid radiochemical method for the determination of 0.01–1 meg of lead has been developed. It consists of adding carrier-free ²¹²Pb to the analysed sample, followed by shaking with a standard lead diethyldithiocarbamate solution in carbon tetrachloride. The amount of non-active lead in the sample is determined from activities of the organic and aqueous phases. A 10-fold excess of bismuth and more than 50–100-fold excess of other metals extractable as diethyldithiocarbamates do not interfere in the determination.     

Production cross section of <Superscript>236</Superscript>Th in the interaction of <Superscript>238</Superscript>U with 60 MeV/u <Superscript>18</Superscript>O ions

The neutron-rich target-like isotope ²³⁶Th has been produced in the ²³⁸U-2p multinucleon transfer reaction between a 60 MeV/u ¹⁸O beam and natural ²³⁸U targets. The activities of thorium were determined after radiochemical separation of Th from the mixture of uranium and reaction products. The ²³⁶Th isotope was identified by the characteristic γ-rays of 642.2, 687.6 and 229.6 keV. The production cross section of ²³⁶Th was determined to be 250±50 μb.     

Search of ligands suitable for 212Pb/212Bi in vivo generators

The short half-life of ²¹²Bi and ²¹³Bi limits the application of these radionuclides in α radionuclide therapy. The labeling of biomolecules with ²¹²Pb (mother nuclide of ²¹²Bi) instead of ²¹²Bi or ²¹³Bi has the advantage of obtaining a conjugate with a half-life of 10.6 h, compared with of 60 min for ²¹²Bi or 46 min for ²¹³Bi. Previous attempts to prepare a potential in vivo generator with ²¹²Pb complexed by the DOTA chelator failed, because about 36 % of Bi was reported to escape as a result of the radioactive decay $^{{212}}{\text{Pb}}{\mathop{\longrightarrow}\limits^{\beta ^{ - }}}{^{212}{\text{Bi}}}$ . Herein, we report studies on the stability of the ²¹²Pb complexes with eight selected polydentate ligands, which demonstrate high affinity for 3+ metal cations. From the ligand studied DOTP and BAPTA show a sufficient ²¹²Pb labeling yields but only ²¹²Pb–DOTP complex is stable in isotonic solution of sodium chloride making this way radioactivity level of released ²¹²Bi is below the limit of detection. It should be emphasized that the DOTP complex is stable only in the case when the concentration of free DOTP exceeds 10^?4 M.     

Determination of uranium in thorium matrixes by epithermal neutron activation analysis

Uranium in thorium matrixes or in minerals and ores containing thorium is determined by epithermal neutron activation analysis (ENAA). In some minerals and ores, such as monazite sands, the analysis can be carried out by purely instrumental means with no chemical separation of uranium or thorium from the irradiated matrix. For thorium compound matrixes with very low uranium contents, a rapid radiochemical separation method, based on the retention of uranyl ion on anion-exchange resins, is first carried out, before counting the gamma-ray peaks for²³⁹U in multichannel analysers coupled to NaI(Tl) scintillators or to Ge(Li) detectors.     

A modified method for the sequential determination of 210Po and 210Pb in Ca-rich material using liquid scintillation counting

This research describes methods for the sequential determination of ²¹⁰Pb and ²¹⁰Po activity concentrations in Ca-rich ash samples collected from oil shale-fired power plants in Estonia. The procedure involves digestion of Ca-rich ash samples in a microwave digestion system, radiochemical separation of ²¹⁰Pb and ²¹⁰Po and their measurements. All samples, blanks and standards were measured by liquid scintillation counting (Quantulus 1220). The method was tested using IAEA (International Atomic Energy Agency) RGU-1 and IAEA-444 reference materials. Spectral calibration/peak identification which included the optimization of α/β discrimination system (pulse shape analyser), and recovery have been made by ²⁰⁹Po and ²¹⁰Pb standard solutions.

     

Determination of232Th in human tissues by pre-concentration neutron activation analysis with yield determination using227Th

The accurate and precise determination of²³²Th in biological samples is very important for the development of biokinetic models for thorium and for improving our knowledge on its distribution in human tissues. Radiochemical neutron activation analysis has long been one of the most sensitive methods for the determination of²³²Th. However, these determinations suffer in reliability because recovery information following the separation is not typically available. This information is particularly important for difficult matrices such as human bone where recoveries may be significantly less than unity. Also, the separation of difficult matrices following neutron activation may involve relatively high personal dose from the co-activated matrix. A novel approach for the determination of radiochemical yield has been developed which employs the use of a readily available, gamma-emitting isotope of thorium,²²⁷Th.²²⁷Th, obtained by radiochemical separation from²²⁷Ac, is added to each, dissolved sample prior to separation and the chemical yield determined by gamma-ray spectrometry following the separation. This pre-concentration step is then followed by neutron activation and the²³²Th determined via²³³Pa using gamma-ray spectrometry. Detection limits were approximately an order of magnitude lower than obtained by alpha-spectrometry.